Device for optically scanning and measuring an environment

ABSTRACT

With a device for optically scanning and measuring an environment, which is designed as a laser scanner, with a light emitter, which emits an emission light beam, with a light receiver which receives a reception light beam which is reflected from an object in the environment of the laser scanner or scattered otherwise, and with a control and evaluation unit which, for a multitude of measuring points, determines at least the distance to the object, the laser scanner has a cooling device with a space between a carrying structure and a shell which serves as a housing, said space opening to the outside by means of an air inlet and otherwise being sealed with respect to the interior of the carrying structure and to the shell.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage Application of PCTApplication No. PCT/EP2011/003263, filed on Jul. 1, 2011, which claimsthe benefit of U.S. Provisional Patent Application No. 61/380,417, filedon Sep. 7, 2010, and of pending German Patent Application No. DE 10 2010032 726.3, filed on Jul. 26, 2010, and which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The invention relates to a device for optically scanning and measuringan environment.

By means of a device such as is known for example from German PatentApplication No. DE 20 2006 005 643, and which is designed as a laserscanner, the environment of the laser scanner can be optically scannedand measured.

SUMMARY OF THE INVENTION

Embodiments of the present invention are based on improving a device ofthe type mentioned hereinabove.

According to an embodiment of the present invention, components of alaser scanner are arranged in two parts of a measuring head and in atraverse of a carrying structure which connects the parts. To reduceweight of the laser scanner, a shell is provided as part of a housing,for example, one shell for each of the two parts of the measuring head,wherein the shell can be made of a light material, for example, plasticmaterial, and covers the corresponding components of the laser scannerfor protection. To protect the shell, a yoke is provided, for example,one yoke for each of the shells, which partially covers the outside ofthe shell and which can be made of a light material, for example,aluminum.

The carrying structure, which, for weight purposes, may also be made ofaluminum, and may have walls which serve for fixing the components withthe optics and the rotating mirror. The walls can also close thesemi-open shells. The yoke may extend along the outer edges and/ordiagonally over the outer surfaces of the shell and is fixed to thecarrying structure, for example, at its ends, if and when necessary alsoin its center, at one of the two walls. In addition to the protectivefunction, further functions can also be integrated into the yoke.

The parameters of the laser scanner, particularly temperature, canchange during operation. Comparative measuring is necessary for acorrection. It is suggested to move the spot of the emission light beamtemporarily along a prism which has a known geometry and a knowndistance to the center of the laser scanner. The prism additionally hasat least two different brightness levels and/or colors, to generatedifferent signal levels of the reception light beam. The differentbrightness levels and/or colors may alternate along the direction ofmotion of the spot of the emission light beam.

During the rotation of the mirror, the emission light beam is projectedonto the traverse of the carrying structure once during every turn,without the environment below being able to be measured. As such, theprism is configured at the traverse. A particular geometrical shape,perpendicular to the direction of motion of the spot of the emissionlight beam or in direction of motion, can take account of the imagingproperties of the receiving optics and thus control the resulting signalquality. Through use of the different brightness levels and/or colorsand the known distance of the prism, the control and evaluation unitcarries out a correction of the distance correction.

For assembling the laser scanner the components have mechanical andelectrical interfaces. Particularly between the parts which arerotatable relative to one another, a high precision is required. Thelaser scanner therefore is provided with a swivel-axis module which, asa pre-assembled assembly, is provided with the base resting in thestationary reference system of the laser scanner and with parts whichcan be fixed to the carrying structure of the measuring head which isrotatable relative to the base. The interfaces which are rotatablerelative to one another are then displaced into the interior of theinterface module. The interfaces between the swivel-axis module and thefurther parts of the measuring head can be configured relatively moresimply, so that, when inserting the swivel-axis module, for example,into a receiving slot of the carrying structure, they are closed in thedirection of insertion.

In the laser scanner, the motors for rotating the measuring head and themirror, as well as the control and evaluation unit and the furtherelectronic components generate heat which must be removed. For thispurpose, the laser scanner is provided with an integrated coolingdevice, based on a ventilation. Hereby, the air is led by an air inletinto a space between the carrying structure and the shell, serving as ahousing, from where it gets through a suction duct, which is sealed withrespect to the interior of the carrying structure, into the interior ofthe cooling device. From there, a fan blows the heated-up air through afurther outlet duct, which is sealed with respect to the interior of thecarrying structure, and through an air outlet to the outside. The heatcan thus be removed without impairing the tightness of centralcomponents. One filter at air inlet and air outlet each, avoidsintrusion of dust and coarse dust particles into the spaces and ducts ofthe cooling device. The air inlet and the air outlet are orientated, forexample by means of ribs, in that the air streams point away from eachother, i.e., unintersectedly into directions which are spread apart aspossibly. The suction duct and the outlet duct, having for example arectangular profile, are connected to the housing of the fan in a sealedmanner. Additionally, if required, the ducts can be completely sealed bymeans of suitable plugs. Each of the two shells is semi-open and closedby a wall of the carrying structure, the air inlet and the air outletmeeting exactly one of the two shells, sealed with respect to oneanother and with respect to the space. A sealing of the shells, whichare arranged outside, against the carrying structure thus guarantees acomplete sealing of the laser scanner. In addition to this ventilation,the cooling device is provided with passive cooling elements, forexample cooling fins and/or heat pipes, to transfer heat from sectionsof the interior of the carrying structure to the active coolingelements. This can be the heat from the electronics or, if the carryingstructure is subdivided into two halves which are sealed with respect toone another, the heat from the other half without active coolingelements of the carrying structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below on the basis of anexemplary embodiment illustrated in the drawing, in which

FIG. 1 is a perspective illustration of the laser scanner;

FIG. 2 is a slightly perspective lateral view of the laser scanner;

FIG. 3 is a bottom view of the laser scanner;

FIG. 4 is a section of the laser scanner in the zone of the swivel-axismodule;

FIG. 5 is a perspective partial view of the laser scanner without shell;

FIG. 6 is a partial view of the cooling device with the perspective ofFIG. 5; and

FIG. 7 is a schematic illustration of the laser scanner duringoperation.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the Figures, a laser scanner 10 is provided as a device foroptically scanning and measuring the environment of the laser scanner10. The laser scanner 10 has a measuring head 12 and a base 14. Themeasuring head 12 is mounted on the base 14 as a unit that can berotated about a vertical axis. The measuring head 12 has a rotary mirror16, which can be rotated about a horizontal axis. The intersection pointof the two rotational axes is designated center C₁₀ of the laser scanner10.

The measuring head 12 is further provided with a light emitter 17 foremitting an emission light beam 18. The emission light beam 18 may be alaser beam in the range of approximately 300 to 1600 nm wave length, forexample, 790 nm, 905 nm or less than 400 nm. However, otherelectro-magnetic waves having, for example, a greater wave length can beused. The emission light beam 18 is amplitude-modulated, for example,with a sinusoidal or with a rectangular-waveform modulation signal. Theemission light beam 18 is emitted by the light emitter 17 onto therotary mirror 16, where it is deflected and emitted to the environment.A reception light beam 20 which is reflected in the environment by anobject O or scattered otherwise, is captured again by the rotary mirror16, deflected and directed onto a light receiver 21. The direction ofthe emission light beam 18 and of the reception light beam 20 resultsfrom the angular positions of the rotary mirror 16 and the measuringhead 12, which depend on the positions of their corresponding rotarydrives which, in turn, are registered by one encoder each.

A control and evaluation unit 22 has a data connection to the lightemitter 17 and to the light receiver 21 in measuring head 12, wherebyparts of the unit 22 can be arranged also outside the measuring head 12,for example, a computer connected to the base 14. The control andevaluation unit 22 determines, for a multitude of measuring points X,the distance d between the laser scanner 10 and the illuminated point atobject O, from the propagation time of emission light beam 18 andreception light beam 20. For this purpose, the phase shift between thetwo light beams 18 and 20 can, for example, be determined and evaluated.

Scanning takes place along a circle by the relatively quick rotation ofthe rotary mirror 16. By virtue of the relatively slow rotation of themeasuring head 12 relative to the base 14, the whole space is scannedstep by step, for example, by the circles. The entity of measuringpoints X of such a measurement is designated scan. For such a scan, thecenter C₁₀ of the laser scanner 10 defines the origin of the localstationary reference system. The base 14 rests in this local stationaryreference system.

In addition to the distance d to the center C₁₀ of the laser scanner 10,each measuring point X comprises a brightness information which isdetermined by the control and evaluation unit 22 as well. The brightnessvalue is a gray-tone value which is determined, for example, byintegration of the bandpass-filtered and amplified signal of the lightreceiver 21 over a measuring period which is attributed to the measuringpoint X. A color camera can optionally generate pictures, by means ofwhich colors (R,G,B) can be assigned to the measuring points as values.

A display device 24 is connected to the control and evaluation unit 22.The display device 24 is integrated into the laser scanner 10, forexample, into the measuring head 12. The display device 24 shows apreview of the scan.

The laser scanner 10 has a carrying structure 30 which serves as theskeleton of the measuring head 12 and at which different components ofthe laser scanner 10 are fixed. In an embodiment, the metal carryingstructure 30 is made of aluminum and in one piece. Above the base 14,the carrying structure 30 has a traverse 30 a which is visible fromoutside and which, at both ends, carries two walls 30 b, which areparallel to one another and project upwards from the traverse 30 a. Twoshells 32 are configured as a housing which is open to one side, and maybe made of plastic. Each of the two shells 32 covers part of thecomponents of the laser scanner 10 which are fixed to the carryingstructure 30 and is assigned to one of the two walls 30 b, to which itis fixed (sealed with a sealing). The walls 30 b and the shells 32 thusserve as housing of the laser scanner 10.

On the outer side of each of the two shells 32, a metal yoke 34 isarranged, which partially covers and thus protects the assigned shell32. Each yoke 34 is fixed to the carrying structure 30, for example, onthe bottom of the traverse 30 a. In an embodiment, each yoke 34 is madeof aluminum and screwed to the traverse 30 a at the side of the base 14.Each yoke 34 extends from its fixing point at the bottom of the traverse30 a obliquely to the next outer corner of the assigned shell 32, fromwhere it extends along the outer edge of shell 32 to the outer corner ofshell 32 which is above, on the upper side of shell 32 obliquely up tothe wall 30 b, a short distance along it (maybe with an additionalfixing point), and then mirror-symmetrically to the described course onthe upper side of shell 32, obliquely to the other outer corner, alongthe outer edge of shell 32 to the outer corner of shell 32 which isbelow and obliquely to the other fastening point at the bottom side oftraverse 30 a.

The two yokes 34 together circumscribe a convex space, within which thetwo shells 32 are completely arranged, i.e., the two yokes 34 togetherproject over all outer edges and outer surfaces of the shells 32. On topand on the bottom the oblique sections of the yokes 34 project over thetop and/or bottom of the shells 32, on the four other sides, twosections each extending along an outer edge of the shells 32. The shells32 are thus protected extensively. Although each of the yokes 34primarily has a protective function, particularly with respect toimpacts which might damage the shells 32 and the components of the laserscanner 10 which are arranged below, further functions can be integratedin one or both of the yokes 34, for example, a gripping possibility forcarrying the laser scanner 10 and/or an illumination.

On top of the traverse 30 a a prism 36 is provided, which extendsparallel to the walls 30 b. In an embodiment, the prism 36 is anintegrally formed (i.e., designed in one piece) component of thecarrying structure 30, but a separate formation and fastening to thetraverse 30 a is conceivable as well. When the mirror 16 rotates, itdirects the emission light beam 18 onto the traverse, and more preciselyonto the prism 36, once during each rotation, and moves the spot whichis generated by the emission light beam 18, along the prism 36.Perpendicularly to the sense of movement of the spot of emission lightbeam 18, the profile of the prism 36 is designed such that, from the topof the traverse 30 a, two trapezoids pointing downwards are designed,from which an isosceles triangle pointing upwards projects. Usually, thespot of the emission light beam 18 is so small that is hits the top ofthe triangle, but illuminates the sides only partially. The surface ofthe prism 36 is designed such that at least two different brightnesslevels and/or colors are provided along the direction of motion of thespot of emission light beam 18. For example, the half which isilluminated first can have a high brightness level (light grey, white),and the half which is illuminated next a low brightness level (darkgrey, black). A reverse order or a striped pattern with several changesof the brightness level is possible as well.

Due to non-linearities in the electronic components, for example, in thelight receiver 21, the measured distances d depend on signal intensity,i.e., brightness, temperature and further parameters. A distancecorrection, which is stored as a function of brightness and isnon-linear, is therefore necessary. Since the prism 36 has a knowndistance d and known brightness levels, a correction of the distancecorrection can be performed by the prism 36, for example, online, i.e.,during operation the influence of temperature and other parameters canbe compensated. At the points corresponding to the brightness levels ofthe prism 36, the difference between the known distance and measureddistance is determined. The correction of the distance correction isperformed by adapting the curve of distance correction to the determineddifference. This correction of distance correction preferably takesplace in the control and evaluation unit 22.

The traverse 30 a has a receiving slot which is open at the bottom, andinto which a swivel-axis module 40 is introduced. The swivel-axis module40 is a pre-assembled assembly which comprises parts which are to befixed at the carrying structure 30 and the base 14 which is rotatable inrelation to the parts and parts which are fixed to it. The base 14 isprovided with a dome 14 a which protrudes upward. A sealing 41 isinterposed between the dome 14 a and the carrying structure 30. A swivelaxis 42 which protrudes vertically upward is fixed to the dome 14 a, forexample, screwed. A horizontally arranged worm gearing 44 is fixed tothe swivel axis 42. The swivel axis 42 has an inner head 46 which, by acrossed roller bearing 47, bears an outer head 48. A horizontallyarranged encoder disk 50 is fixed to the upper end of the inner head 46,above which the outer head 48 has encoder read heads 52. Besides, sliprings 54 for the internal (i.e., which takes place within theswivel-axis module 40) transmission of data and energy of power supplyare provided between the inner head 46 and the outer head 48. At theupper end of the outer head 48 and at the lower end of the base 14,electric plug connectors 55 for the transmission of data and energy fromand to the measuring head 12 are provided.

For interaction with the worm gearing 44 a motor 56 with a planetarygear 57 is provided, which is borne in the carrying structure 30 andwhich drives a worm 58 which meshes with the worm gearing 44. Thedescribed swivel-axis module 40 is introduced into the traverse 30 a, sothat the plug connectors 55 at the outer head 48 are plugged togetherwith suitable counter-contacts, the worm 58 meshes with the worm gearing44, the outer head 48 can be fixed to the carrying structure 30 and asealing 59 comes to lie between the base 14 and the carrying structure30. In the swivel-axis module 40, the swivel axis 42, the worm gearing44, the inner head 46 and the encoder disk 50 are fixed to the base 14,while, rotatably relative to this, the outer head 48 and the encoderread heads 52 are fixed to the carrying structure 30, and the motor 56with the planetary gear 57 and the worm 58 are borne. The measuring head12 is thus rotatable about a vertical axis, relative to the base 14.

The laser scanner 10 has an integrated cooling device 70 which cools bymeans of air flowing through sealed ducts. The cooling device 70comprises a suction duct 72 which preferably is designed with arectangular profile, a fan 74 and an outlet duct 76 which preferably isdesigned with a rectangular profile as well. The fan 74 with its housingis connected to the suction duct 72 and to the outlet duct 76 in asealed manner. The suction duct 72 is arranged between the motor 56 forthe swiveling movement of the measuring head 12 and a motor for therotation of the mirror 16 which is arranged above. The outlet duct 76 isarranged between the motor 56 and the electronics.

The suction duct 72 opens to a largely sealed space Z between thecarrying structure 30 and the shell 32. The sealing of the space Z withrespect to the interior of the carrying structure 30 prevents intrusionof dirt and dust into the interior of the carrying structure. Thecarrying structure 30 has cooling fins 78 next to the motor 56, whichtransfer the heat from the interior of the carrying structure 30 intothe space Z. From outside, the air gets over an air inlet 80, forexample, a ventilation grille with ribs, into the space Z. A filter, forexample a filter mat, at the air inlet 80 prevents intrusion of coarsedust particles and dust into the space Z.

The outlet duct 76 terminates, sealed with respect to the space Z, at anair outlet 82, for example, a ventilation grille with ribs. The airinlet 80 and the air outlet 82 are spaced apart from each other and, inthe present case, are separated by the yoke 34 and configured on thebottom of the shell 32. The ribs of the ventilation grilles are alignedsuch that the air flow to the air inlet 80 and from the air outlet 82point away from one another, i.e., no heated-up air is sucked in.Additionally, a heat pipe extends between the area of the measuring head12 with the control and evaluation unit 22 and the suction duct 72, theheat pipe transferring heat to the cooling device 70 as well. The fan 74sucks in air via the air inlet 80, the space Z and the suction duct 72and blows the air again out of the laser scanner 10, via the outlet duct76 and the air outlet 82. Cooling thus takes place.

The laser scanner 10 may have different sensors, for example,thermometer, inclinometer, altimeter, compass, gyroscopic compass, GPS,etc., which are connected to the control and evaluation unit 22. By suchsensors the operating conditions of the laser scanner 10 are monitored,which are defined by certain parameters, for example, geometricorientation or temperature. If one or several parameters have a drift,this is recognized by the corresponding sensors and can be compensatedby the control and evaluation unit 22. By such sensors, also a suddenchange of operating conditions can be recognized, for example, an impacton the laser scanner 10 which changes its orientation, or a displacementof the laser scanner 10. If the extent of the changes cannot beregistered with sufficient precision, the scanning process must beinterrupted or aborted. If the extent of the changes of operatingconditions can be roughly estimated, the measuring head 12 can be turnedback by some angular degrees until there is an overlapping with the areawhich has been scanned before the sudden change, and the scanningprocess continues. The two different parts of the scan can be assembledby an evaluation of the overlapping area.

The invention claimed is:
 1. Device for optically scanning and measuringan environment, said device being designed as a laser scannercomprising: a light emitter, which emits an emission light beam, a lightreceiver which receives a reception light beam which is a portion of theemission light beam reflected from an object in the environment, and acontrol and evaluation unit connected to the light receiver which, for amultitude of measuring points, determines a distance to the object,wherein the laser scanner is provided with a carrying, a shell servingas an outer housing, and a cooling device, said cooling device furthercomprising an air inlet, a space between the carrying structure and theshell, said space opening to the environment by means of the air inletand otherwise being sealed with respect to an interior of the carryingstructure and to the shell, a suction duct opening to the space betweenthe carrying structure and the shell, an outlet duct, a fan having a fanhousing connected to the suction duct and to the outlet duct in a sealedmanner, an air outlet at which the outlet duct terminates sealed withrespect to the space, wherein the fan sucks in air through the airinlet, pulls the air through the space and the suction duct, and blowsthe air out of the laser scanner through the outlet duct and the airoutlet.
 2. Device according to claim 1, characterized in that passivecooling elements, particularly cooling fins and/or heat conduits areprovided, which are connected to the active cooling elements of thecooling device and thus cool sections of the interior of the carryingstructure.
 3. Device according to claim 1, characterized in that the airinlet and the air outlet are spaced apart from each other and alignedand/or provided with ribs in such a way that the air flows to the airinlet and from the air outlet point away from one another.
 4. Deviceaccording to claim 1, characterized in that, as part of the housing ofthe laser scanner, at least one shell is provided, which partially iscovered at its outer side by at least one yoke serving as protection,and/or that the emission light beam temporarily moves along a prism ofthe laser scanner, said prism having at least two different brightnesslevels and/or colors.
 5. Device according to claim 1, characterized inthat the laser scanner is provided with a swivel-axis module which, as apre-assembled assembly, on the one hand is provided with a base restingin the stationary reference system of the laser scanner and, on theother hand, with parts that can be fixed to the carrying structure of ameasuring head which is rotatable relative to the base.